Switch circuit

Abstract

A switch circuit for controlling the supply of electrical power from an electrical power source to a load includes a power supply switch comprising input, output and control terminals. The circuit further includes an electronic switching device connected to the control terminal of the power supply switch and having an activating input; a momentary switch coupled to the activating input of the electronic switching device; and a charge storage element coupled to the momentary switch. In a first mode, closing the momentary switch in excess of a triggering time charges the charge storage element and triggers the electronic storage device to turn on the circuit to supply power to the load. In a second mode, closing the momentary switch connects the charge storage element to the electronic switching device to turn off the electronic switching device and the power supply switch, thus interrupting the supply of power to the load.

1. A switch circuit for controlling the supply of electrical power from an electrical power source to a load, the switch circuit comprising
 a power supply switch having input, output and control terminals, wherein the input terminal of the power supply switch is coupled to the electrical power source and the output terminal of the power supply switch is coupled to the load; 
 an electronic switching device connected to the control terminal of the power supply switch and having an activating input; 
 a momentary switch coupled to the activating input of the electronic switching device; 
 a charge storage element coupled to the momentary switch; 
 the arrangement being such that 
 (i) in a first mode, power is supplied to the load by closing the momentary switch to connect the charge storage element to the electronic switching device for a predetermined time in excess of a triggering time of the electronic switching device, the predetermined time being determined by the charge-up time of the charge storage element and triggering of the electronic switching device maintaining the power supply switch in an on state to supply power from the electrical power source to the load; and 
 ii) in a second mode, the supply of power to the load is stopped by closing the momentary switch to connect the charge storage element to the electronic switching device, the charge storage element providing a signal to turn off the electronic switching device and the power supply switch to cut the supply of power from the electrical power source to the load. 
 
   
   
     2. A switch circuit according to  claim 1 , wherein the electronic switching device comprises a thyristor device. 
   
   
     3. A switch circuit according to  claim 1  wherein the power supply switch comprises a transistor. 
   
   
     4. A switch circuit as claimed in  claim 1  wherein the electronic switching device and/or power supply switch are formed from at least one bipolar transistor. 
   
   
     5. A switch circuit as claimed in  claim 1  wherein the electronic switching device and/or power supply switch are formed from at least one MOSFET. 
   
   
     6. A switch circuit according to  claim 1 , wherein the power supply switch and the electronic switching device are assembled together on an integrated circuit. 
   
   
     7. A switch circuit according to  claim 1 , wherein the charge storage element comprises a capacitor. 
   
   
     8. A switch circuit as claimed in  claim 1  further comprising a charge-up time controller for the charge storage element. 
   
   
     9. A switch circuit as claimed in  claim 8  wherein the charge-up time controller comprises a resistive element. 
   
   
     10. A switch circuit as claimed in  claim 9  wherein the charge storage element and charge-up time controller are disposed in series and across the load. 
   
   
     11. A switch circuit as claimed in  claim 10  wherein the momentary switch is connected between the charge storage element and the charge-up time controller. 
   
   
     12. A switch circuit according to  claim 8 , wherein the power supply switch, electronic switching device and charge-up time controller are assembled together on an integrated circuit. 
   
   
     13. An integrated circuit for controlling the supply of electrical power from an electrical power source to a load, the integrated circuit comprising
 means for receiving a supply of electrical power from an electrical power source; 
 a first connection means arranged to connect the integrated circuit to a load; 
 a second connection means arranged to connect the integrated circuit to a charge storage element, wherein the second connection means is coupled to the first connection means; 
 a power supply switch having input, output and control terminals, wherein the input terminal of the power supply switch is coupled to the means for receiving a supply of electrical power and the output terminal of the power supply switch is coupled to the first connection means; 
 an electronic switching device connected to the control terminal of the power supply switch and having an activating input arranged to connect the integrated circuit to a momentary switch; 
 the arrangement being such that 
 (i) in a first mode, power is able to be supplied to a said load by closing a said momentary switch to connect to the electronic switching device for a predetermined time in excess of a triggering time of the electronic switching device a said charge storage element disposed in series with the said momentary switch, the predetermined time being determined by the charge-up time of the said charge storage element and triggering of the electronic switching device maintaining the power supply switch in an on state to supply power from the said electrical power source to the said load; and 
 ii) in a second mode, the supply of power to the said load is stopped by closing the said momentary switch to connect the said charge storage element to the electronic switching device, the said charge storage element providing a signal to turn off the electronic switching device and the power supply switch to cut the supply of power from the said electrical power source to the said load. 
 
   
   
     14. An integrated circuit according to  claim 13  further comprising a charge-up time controller for controlling the charge-up time of the said charge storage element. 
   
   
     15. An integrated circuit according to  claim 14 , wherein the charge-up time controller comprises a resistive element. 
   
   
     16. An integrated circuit according to  claim 14 , wherein the charge-up time controller is connected between the first and second connection means such that the charge-up time controller and the said charge storage element are disposed in series and across the said load. 
   
   
     17. A combination of an integrated circuit according to  claim 13  and a momentary switch connected to the activating input in which the integrated circuit and momentary switch are packaged integrally. 
   
   
     18. A combination according to  claim 17  in which the integrated circuit is mounted on a packaging substrate and the integrated circuit and momentary switch are encapsulated in an electrically insulating material, the momentary switch protruding out of the electrically insulating material so that it can be actuated externally.